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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is grahams law

A

Rate of diffusion is inversely proportional to the square root of the MW of a substance

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2
Q

What is first pass metabolism

A

Where the concentration of a drug is reduced before it reaches the systemic circulation by gut/liver.

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3
Q

Extraction ratio?

A

Fraction of a drug removed by an organ on each pass through that organ

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4
Q

Drugs with hig extraction ratio? (>0.7)

A

Propanolol
Lidocaine
GTN
TCA
Opiods

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5
Q

Drugs with intermediate extraction ratio? (0.3-0.7)

A

Midazolam
More dependent on enzyme activity

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6
Q

Low extraction ratio drugs? (<0.3)

A

-Capacity dependent clearance=sensitive to protein binding/enzyme limited/senstive to changes in enzyme. Blood flow will not really affect how much extracted

EG thiopentone, phenytoin, warfarin

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7
Q

What is bioavailability?

A

The amount of drug that reaches the systemic circulation compared to that given IV

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8
Q

What affects bioavailability?

A
  • absorption from whichever route
  • Drug loss from gut lumen (diarrhoea/mucosa issues)
  • Metabolism in gut wall/first pass

-Poor lipid solubility
-High molecular weight

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9
Q

WHat is distribution

A

TRansfer of drug dfrom site of absorption to other tissues about the body

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10
Q

What factors affect distribution

A

-Protein binding
- blood flow
MW
ionisation
conc. gradient

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11
Q

What is clearance

A

The volume of plasma cleared of drug per unit time

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12
Q

what is metabolism

A

Conversion of drugs from one form to another that can be eliminated from the body

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13
Q

Examples of phase one reactions

A

Oxudation
HYdrolysis
Reduction

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14
Q

What is the purpose of phase 2 reactions

A

Increase water solubility to allow excretion by kidneys/bile

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15
Q

Examples of phase 2 reactions

A

Conjugation with glycine/sulfate/glucuronic acid

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16
Q

Where are the largest quantites of Cytochrome oxidase P450 found

A

SER of the liver

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17
Q

What is elimination

A

The removal of drug from body (by metabolism or excretion)

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18
Q

What is excretion

A

The removal of unchanged drug or metabolites from the body ( a form of elimination)

19
Q

WHat is eulers number

A

base of natural log, base rate of growth shared by all continually growing processes
(base rate of change of an exponential process)

20
Q

FActors affecting half life?

A

-Increased Vd increases half life
- Decreasing clearance increases half life

21
Q

Fentanyl pKA

A

Weak base
pKa 8.4 (entirly ionised in the stomach)

22
Q

Diclofenac pKA

A

Weak acid, pKA of 4

23
Q

Why is absorption from the small bowel more important than stomach for most oral meds?

A

Greater absorptive area = greater proportion of absorption

24
Q

WHere can thiopental be given in the GI tract?

A

REctally

25
Q

Why cant atracurium be given orally?

A

Bis-quaternary molecule that is permanently charged and not absorbed from the GI tract

26
Q

Why is physostigmine better absorbed than neostigmine?

A

Neostigmine is quaternary and charged, physostigmine is a tertiary amine

27
Q

WHat determines binding to albumin/alpha 1 acid glycoprotein?

A

Acidic/neutral drugs bind to albuin
Basic drugs or those with a quaternart nitrogen bind to a1a glycoprotein

28
Q

Basic drugs?

A

Fentanyl
Lidocaine

29
Q

Acidic drugs?

A

Ibuprofen

30
Q

Neutral drugs?

A

DIazepam
Phenytoin

31
Q

Why do amiodarone and warfarin interact?

A

Amiodarone inhibits CYP2C9

32
Q

non depolarising muscle relaxants Vd?

A

SMall- charged + do not cross lipid membranes

33
Q

Propofol Vd

A

Large- estimated at 20-60L/kg (at least 4 even with short infusions)
Essentially unionised at plasma pH + v lipid soluble

34
Q

Metabolites of atracurium

A

Laudanosine (minor hoffman pathway)
Monoquaternary alcohol derivative (major ester hydrolysis pathway)

35
Q

Enzymes showing pharmacogenetic variations

A

CYP2D6 (codeine)
CYP2C9 (Warfarin)

36
Q

Drugs with high oral bioavailability?

A

Paracetamol (90)
Ibuprofen (>80)

37
Q

Drugs with poor bioavailability?

A

Aspirin (65)
Oramorph (25)
Diclofenac (50)

38
Q

What breaks down remifentanyl?

A

Tissue esterases (+ plasma esterase, but less important)

39
Q

Why does dobutamine increase hepatic extraction of propofol?

A

INcreases hepatic blood flow

40
Q

What enzymes are involved in propofol metabolism

A

CYP2B6 + CYP2C9

41
Q

WHy doesnt carbamazepine increase hepatic extraction of propofol?

A

Induces CYP enzymes, but the hepatic ER is already almost 1

42
Q

Drugs with small volumes of distribution?

A

Permanently charged molecules (do not distribute across lipid membranes) / lipid insoluble/rapidly metabolised/ionised at body pH

43
Q

What affects drugs crossing the placenta?

A

Drugs that are lipid soluble cross the placenta more rapidly than drugs that are ionised at plasma pH
Drugs that are permanently charged do not cross the placenta

Pharmacology (12 decks)

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